Optical pickup device and optical element used for the same

ABSTRACT

An optical pickup device, comprises light sources to emit a first light flux having a wavelength λ 1  (380 nm&lt;λ 1 &lt;450 nm); a second light flux having a wavelength λ 2  (600 nm&lt;λ 2 &lt;700 nm); and a light-converging optical system. The light-converging optical system converges the first light flux on a first optical information recording medium through a protective layer having a thickness t 1  and the light-converging optical system converges the second light flux on a second optical information recording medium through a protective layer having a thickness t 2 . The light-converging optical system forms a first spot on the information recording surface of the first optical information recording medium by using N-th order diffracted light ray generated, and the light-converging optical system forms a second spot on the information recording surface of the second optical information recording medium by using M-th order (M≠N) diffracted light ray generated.

BACKGROUND OF THE INVENTION

The present invention relates to an optical pickup device and an opticalelement used for the optical pickup device, and in particular, to anoptical pickup device capable of recording and/or reproducinginformation by the use of a violet laser or lasers other than the violetlaser and to an optical element used for the optical pickup device.

Backed by practical application of a short wave red semiconductor laser,there has recently been developed and commercialized DVD (digitalversatile disk) representing a high density optical disk which issimilar to CD (compact disk) representing a conventional optical disk(also called an optical information recording medium) in terms of a sizeand has a greater capacity, and it is estimated that an advanced opticaldisk having higher density will appear in the near future. In thelight-converging optical system of an optical information recording andreproducing apparatus (also called an optical pickup device) whereinsuch advanced optical disk is a medium, a diameter of a spot convergedon an information recording surface through an objective lens isrequired to be small, for the purpose of achieving higher density ofrecording signals, or for reproducing higher density recording signals.For that purpose, a short wavelength of a laser representing a lightsource and a higher numerical aperture of the objective lens arerequired. What is expected in terms of practical use as a shortwavelength laser light source is a violet semiconductor laser with awavelength of about 400 nm.

There have been advanced studies and developments of a high density disksystem capable of conducting recording/reproducing by the use of thisviolet semiconductor laser with a wavelength of about 400 nm. As anexample, in the case of the optical disk conductingrecording/reproducing information under the specifications of NA 0.85and wavelength of 405 nm (hereinafter referred to as “high density DVD”in the specification), information of 20–30 GB per one surface can berecorded for the optical disk having a diameter of 12 cm which is thesame as DVD (NA 0.6, light source wavelength 650 nm, storage capacity4.7 GB) in size.

When an objective lens having high NA is made to be a plastic lens in anoptical pickup device for high density DVD, there is generated sphericalaberration caused by changes in the refractive index resulting fromtemperature changes, which is a problem. The problem of this kind iscaused by a plastic lens which is greater than a glass lens bymagnifying power of a two-digit number in terms of a change of therefractive index resulting from temperature changes. Since thistemperature aberration is proportional to the fourth power of NA, whenan objective lens having NA of 0.85 to be used for high density DVD ismade to be a plastic lens, a range of temperatures which can be used forthat lens is reduced to be extremely narrow, which is a problem for thepractical use of the lens. Further, since a semiconductor laseroriginally causes a wavelength fluctuation phenomenon which is called amode hop, it is necessary to control aberration in a converging spot onan information recording surface, even when a mode hop is caused. Inaddition, there is generally dispersion of oscillation wavelengthbetween individuals of a semiconductor laser, and even in the case of acombination of semiconductor lasers having dispersion to a certainextent and objective lenses, it is necessary to form a converging spotwhich is appropriate to a level that makes recording/reproducing ofinformation possible. For that purpose, spherical aberration caused byfluctuations of light source wavelength needs to be controlled by somemethods or other.

Further, value of the optical pickup device as a product is notsufficient if the optical pickup device cannot conduct more thanrecording/reproducing information properly for high density DVD. Whenconsidering that DVDs having therein various types of informationrecorded are on the market presently, recording/reproducing informationproperly for high density DVD only is not enough, and the value of theproduct as an optical pickup device of an interchangeable type isenhanced, by achieving that recording/reproducing of information canequally be conducted properly for conventional DVDs owned by, forexample, a user. From the background mentioned above, it is necessary,with respect to a light-converging optical system used for an opticalpickup device of an interchangeable type, to control properly all ofaberration deterioration caused by temperature changes, aberrationdeterioration caused by wavelength fluctuations and aberrationdeterioration in the case of a mode hop (or chromatic aberration), onthe converging spot formed on the information recording surface whenrecording/reproducing information for high density DVD, and it isnecessary to control properly all of aberration deterioration caused bytemperature changes, aberration deterioration caused by wavelengthfluctuations and aberration deterioration in the case of a mode hop (orchromatic aberration), on the converging spot formed on the informationrecording surface when recording/reproducing information forconventional DVD. However, it is extremely difficult to satisfy aplurality of aberration conditions with a single light-convergingoptical system. Nevertheless, if two light-converging optical systemseach having an objective lens are provided for converging a violet laserbeam and a conventional laser beam separately, an optical pickup deviceis made to be large in size, and its cost is increased, which is aproblem. Incidentally, the structure for converging a violet laser beamand a conventional laser beam with a single light-converging opticalsystem is disclosed in the following patent document, but there is nodisclosure about a design to consider temperature characteristics andwavelength characteristics.

SUMMARY OF THE INVENTION

The invention has been achieved in view of the problems mentioned above,and its object is to provide an optical pickup device which has acompact structure and yet is capable of conducting recording andreproducing of information properly for high density DVD or for both thehigh density DVD and a conventional DVD, and to provide an opticalsystem which can be used for the optical pickup device.

The optical pickup device described in Item 1 is represented by anoptical pickup device that has therein a first light source havingwavelength λ1 (380 nm<λ1<450 nm), a second light source havingwavelength λ2 (600 nm<λ2<700 nm) and a light-converging optical systemhaving a light-converging optical element including a diffractivestructure and a correcting element arranged between the first lightsource and/or the second light source and the light-converging opticalelement, and is capable of conducting recording and/or reproducinginformation when the light-converging optical system converges a lightflux emitted from the first light source on an information recordingsurface of the first optical information recording medium through aprotective layer having thickness t1, and is capable of conductingrecording and/or reproducing information when the light-convergingoptical system converges a light flux emitted from the second lightsource on an information recording surface of the second opticalinformation recording medium through a protective layer having thicknesst2, wherein the first spot is formed on the information recordingsurface of the first optical information recording medium by the use ofN-th order diffracted light that is generated when a light flux from thefirst light source passes through the diffractive structure of thelight-converging optical system, and the second spot is formed on theinformation recording surface of the second optical informationrecording medium by the use of M (M≠N)-th order diffracted light that isgenerated when a light flux from the second light source passes throughthe diffractive structure of the light-converging optical system, while,spherical aberration deteriorated by wavelength changes in the firstlight source and spherical aberration deteriorated by temperaturechanges are controlled to be in a range necessary for recording and/orreproducing of information on the first spot formed on the informationrecording surface of the first optical information recording medium, andspherical aberration deteriorated by wavelength changes in the secondlight source and spherical aberration deteriorated by temperaturechanges are controlled to be in a range necessary for recording and/orreproducing of information on the second spot formed on the informationrecording surface of the second optical information recording medium.Namely, in view of the actual circumstances that it is difficult for asingle light-converging optical element to form a converging spot thatis free from aberration deterioration on each condition, for both of thelight flux from the light source with wavelength λ1 and a light fluxfrom the light source with wavelength λ2, the diffractive structure onthe light-converging optical element and the correction element are usedin the invention to control each aberration deterioration in awell-balanced way, thus, recording and/or reproducing of information isconducted properly for both of the high density DVD and the conventionalDVD. Incidentally, as stated later, the correction element includes anoccasion to make only the light flux emitted from the first light sourceto pass, an occasion to make only the light flux emitted from the firstlight source to pass and an occasion to make light fluxes emitted fromboth light sources to pass respectively.

In the optical pickup device described in Item 2, chromatic aberrationof the converging spot caused by changes in a wavelength of a lightsource is controlled to be within a range necessary for recordingand/reproducing of information in the first spot formed on aninformation recording surface of the first optical information recordingmedium, and chromatic aberration of the converging spot caused bychanges in a wavelength of a light source is controlled to be within arange necessary for recording and/reproducing of information in thesecond spot formed on an information recording surface of the secondoptical information recording medium, thus, the optical pickup devicecan conduct recording and/or reproducing of information properly forboth a high density DVD and a conventional DVD, for example.

In the optical pickup device described in Item 3, it is preferable thatt1 representing a thickness of a protective layer of the first opticalinformation recording medium and t2 representing a thickness of aprotective layer of the second optical information recording mediumsatisfy the following expressions.0.5 mm≦t1≦0.7 mm  (1)0.5 mm≦t2≦0.7 mm  (2)

It is preferable for the optical pickup device described in Item 4 thatthe aforementioned diffractive structure is provided on the area throughwhich light fluxes pass commonly when conducting recording and/orreproducing of information for the first optical information recordingmedium and the second optical information recording medium, in a part ofat least one optical surface of the light-converging optical element,diffraction efficiency of 3m-th (m represents a positive integer, and soforth) order diffracted light becomes higher than diffraction efficiencyof another order diffracted light generated when a light flux emittedfrom the first light source passes, and diffraction efficiency of 2m-thorder diffracted light becomes higher than diffraction efficiency ofanother order diffracted light that is generated when a light fluxemitted from the second light source passes.

It is preferable for the optical pickup device described in Item 5 thatthe aforementioned diffractive structure is provided on the area throughwhich light fluxes pass commonly when conducting recording and/orreproducing of information for the first optical information recordingmedium and the second optical information recording medium, in a part ofat least one optical surface of the light-converging optical element,diffraction efficiency of 8p-th (p represents a positive integer, and soforth) order diffracted light becomes higher than diffraction efficiencyof another order diffracted light generated when a light flux emittedfrom the first light source passes, and diffraction efficiency of 5p-thorder diffracted light becomes higher than diffraction efficiency ofanother order diffracted light that is generated when a light fluxemitted from the second light source passes.

It is preferable for the optical pickup device described in Item 6 thatthe aforementioned diffractive structure is provided on the area throughwhich light fluxes pass commonly when conducting recording and/orreproducing of information for the first optical information recordingmedium and the second optical information recording medium, in a part ofat least one optical surface of the light-converging optical element,diffraction efficiency of 2n-th (n represents a positive integer, and soforth) order diffracted light becomes higher than diffraction efficiencyof another order diffracted light generated when a light flux emittedfrom the first light source passes, and diffraction efficiency of n-thorder diffracted light becomes higher than diffraction efficiency ofanother order diffracted light that is generated when a light fluxemitted from the second light source passes.

It is preferable for the optical pickup device described in Item 7 thatthe correction element is arranged in an optical path through which onlythe light flux emitted from the first light source passes, or arrangedin an optical path through which only the light flux emitted from thesecond light source passes.

It is preferable for the optical pickup device described in Item 8 thatthe correction element is arranged in an optical path through which onlythe light flux emitted from the second light source passes, chromaticaberration of a light convergence spot in the case of a change of awavelength of a light source on the first spot formed on an informationrecording surface of the first information recording medium iscontrolled by the aforesaid light-converging optical element within arange necessary for recording and/or reproducing of information, andchromatic aberration of a light convergence spot in the case of a changeof a wavelength of a light source on the second spot formed on aninformation recording surface of the second information recording mediumis controlled by the aforesaid light-converging optical element within arange necessary for recording and/or reproducing of information.

It is preferable for the optical pickup device described in Item 9 thatthe following expression is satisfied by the number N1 of a diffractivering-shaped zones existing on an area where light fluxes pass throughcommonly when conducting recording and/or reproducing information forthe first optical information recording medium and the second opticalinformation recording medium, among diffractive structures provided onthe light-converging optical element;115/A≦N1≦155/A  (3)(wherein, A represents 3m or 8p which is the order wherein diffractionefficiency in a light flux having wavelength λ1 is higher than that ingenerated diffracted light having another order).

It is preferable for the optical pickup device described in Item 10 thatthe correction element has a diffractive structure on at least oneoptical surface thereof, and the following expression is satisfied bythe number N2 of a diffractive ring-shaped zones in the diffractivestructure on the correction element;15/k≦N2≦45/k  (4)(wherein, k represents the order wherein diffraction efficiency in alight flux having wavelength λ2 is higher than diffraction efficiency ofgenerated diffracted light having another order).

It is preferable for the optical pickup device described in Item 11 thatthe diffracting power of the diffractive structure of the correctionelement is positive.

It is preferable for the optical pickup device described in Item 12 thatthe correction element is arranged in an optical path through which onlythe light flux emitted from the first light source passes, chromaticaberration of a light convergence spot in the case of a change of awavelength of a light source on the first spot formed on an informationrecording surface of the first information recording medium iscontrolled by the aforesaid correction element within a range necessaryfor recording and/or reproducing of information, and chromaticaberration of a light convergence spot in the case of a change of awavelength of a light source on the second spot formed on an informationrecording surface of the second information recording medium iscontrolled by the aforesaid light-converging optical element within arange necessary for recording and/or reproducing of information.

It is preferable for the optical pickup device described in Item 13 thatthe following expression is satisfied by the number N1 of a diffractivering-shaped zones existing on an area where light fluxes pass throughcommonly when conducting recording and/or reproducing information forthe first optical information recording medium and the second opticalinformation recording medium, among diffractive structures provided onthe light-converging optical element;45/A≦N1≦65/A  (5)(wherein, A represents 3m or 8p which is the order wherein diffractionefficiency in a light flux having wavelength λ1 is higher than that ingenerated diffracted light having another order).

It is preferable for the optical pickup device described in Item 14 thatthe correction element has a diffractive structure on at least oneoptical surface thereof, and the following expression is satisfied bythe number N2 of a diffractive ring-shaped zones in the diffractivestructure on the correction element;30/k≦N2≦80/k  (6)(wherein, k represents the order wherein diffraction efficiency in alight flux having wavelength λ2 is higher than diffraction efficiency ofgenerated diffracted light having another order).

It is preferable for the optical pickup device described in Item 15 thatthe diffracting power of the diffractive structure of the correctionelement is negative.

It is preferable for the optical pickup device described in Item 16 thatthe correction element is arranged in an optical path through which alight flux emitted from the first light source passes and is arranged inan optical path through which a light flux emitted from the second lightsource passes.

It is preferable for the optical pickup device described in Item 17 thatchromatic aberration of a light convergence spot in the case of a changeof a wavelength of a light source on the first spot formed on aninformation recording surface of the first information recording mediumand on the second spot formed on an information recording surface of thesecond information recording medium is controlled by thelight-converging optical element within a range necessary for recordingand/or reproducing information, and spherical aberration deteriorated bytemperature changes of the first spot formed on an information recordingsurface of the first information recording medium and of the second spotformed on an information recording surface of the second informationrecording medium is controlled by the correction element within a rangenecessary for recording and/or reproducing information.

It is preferable for the optical pickup device described in Item 18 thatthe following expression is satisfied by the number N1 of a diffractivering-shaped zones existing on an area where light fluxes pass throughcommonly when conducting recording and/or reproducing information forthe first optical information recording medium and the second opticalinformation recording medium, among diffractive structures provided onthe light-converging optical element;144/(2n)≦N1≦176/(2n)  (7)(wherein, 2n represents the order wherein diffraction efficiency in alight flux having wavelength λ1 is higher than that in generateddiffracted light having another order).

It is preferable for the optical pickup device described in Item 19 thatthe correction element has a diffractive structure on at least oneoptical surface thereof, and the following expression is satisfied bythe number N2 of a diffractive ring-shaped zones in the diffractivestructure on the correction element;30/k≦N2≦80/k  (8)(wherein, k represents the order wherein diffraction efficiency in alight flux having wavelength λ2 is higher than diffraction efficiency ofgenerated diffracted light having another order).

It is preferable for the optical pickup device described in Item 20 thatthe diffracting power of the diffractive structure of the correctionelement is positive.

It is preferable for the optical pickup device described in Item 21 thatthe following expression is satisfied by focal length f1 of thelight-converging optical element relating to a light flux emitted fromthe first light source.1.8 mm≦f1≦3.0 mm  (9)

It is preferable for the optical pickup device described in Item 22 thatthe following expression is satisfied by magnification mt wherein thelight-converging optical element and the correction element arecombined.−⅓≦mt≦− 1/10  (10)

It is preferable for the optical pickup device described in Item 23 thatcontrolling of spherical aberration deteriorated by fluctuations of thelight source wavelength means controlling an amount of changes inspherical aberration of wavefront aberration to 0.07 λ rms, when lightsource wavelength λ is changed by 10 nm.

It is preferable for the optical pickup device described in Item 24 thatcontrolling of chromatic aberration of a light convergence spot in thecase of a change in a light source wavelength to a range necessary forrecording and/or reproducing of information means controlling wavefrontaberration to 0.02 λ rms or less at the best image position before thechange when light source wavelength λ is changed by 1 nm.

It is preferable for the optical pickup device described in Item 25 thatcontrolling of spherical aberration deteriorated by temperature changesto a range necessary for recording and/or reproducing of informationmeans controlling an amount of changes in spherical aberration ofwavefront aberration to 0.04 λ rms or less, when a temperature ischanged by 30° C. Incidentally, λ represents a light source wavelengthfor an incident light flux, in the present specification.

It is preferable for the optical pickup device described in Item 26 thatthe following expression is satisfied when NA1 represents a numericalaperture of the light-converging optical element closer to an imagenecessary for conducting recording and/or reproducing of information forthe first optical information recording medium.0.63≦NA1≦0.67  (11)

It is preferable for the optical pickup device described in Item 27 thatthe following expression is satisfied when NA2 represents a numericalaperture of the light-converging optical element closer to an imagenecessary for conducting recording and/or reproducing of information forthe second optical information recording medium.0.63≦NA2≦0.67  (12)

It is preferable for the optical pickup device described in Item 28 thatthe following expression is satisfied when Δλ1/ΔT representsfluctuations of a wavelength for the temperature of the first lightsource.0.03 nm≦Δλ1/ΔT≦0.1 nm  (13)

It is preferable for the optical pickup device described in Item 29 thatthe following expression is satisfied when Δλ2/ΔT representsfluctuations of a wavelength for the temperature of the second lightsource.0.15 nm≦Δλ2/ΔT≦0.25 nm  (14)

It is possible for the optical pickup device described in Item 30 toconduct recording/reproducing of information even for CD in addition tohigh density DVD and conventional DVD, if the optical pickup device hasa third light source with wavelength λ3 (750 nm<λ3<800 nm), and if thelight-converging optical system can conduct recording and/or reproducingof information by converging a divergent light flux emitted from thethird light source on an information recording surface of the thirdoptical information recording medium through a t3-thick protectivelayer.

It is preferable for the optical pickup device described in Item 31 thatoptical system magnification mo of the light-converging optical elementfor an incident light flux with wavelength λ3 satisfies the followingexpression.− 1/12<mo<− 1/14  (15)

It is preferable for the optical pickup device described in Item 32 thatthe optical pickup device has a third light source with wavelength λ3(750 nm<λ3<800 nm), the light-converging optical system can conductrecording and/or reproducing of information by converging a divergentlight flux emitted from the third light source on an informationrecording surface of the third optical information recording mediumthrough a t3-thick protective layer, and a diffraction efficiency of the(3m/2)-th order (3m/2 is an integer) diffracted light is higher thanthat of the other order diffracted light generated, when the light fluxemitted from the third light source passes.

It is preferable for the optical pickup device described in Item 33 thatoptical system magnification mo of the light-converging optical elementfor an incident light flux with wavelength λ3 satisfies the followingexpression.− 1/12<mo<− 1/14  (16)

It is preferable for the optical pickup device described in Item 34 thatthe optical pickup device has a third light source with wavelength λ3(750 nm<λ3<800 nm), the light-converging optical system can conductrecording and/or reproducing of information by converging a divergentlight flux emitted from the third light source on an informationrecording surface of the third optical information recording mediumthrough a t3-thick protective layer, and a diffraction efficiency ofn-th order diffracted light is higher than that of the other orderdiffracted light generated, when the light flux emitted from the thirdlight source passes.

It is preferable for the optical pickup device described in Item 35 thatoptical system magnification mo of the light-converging optical elementfor an incident light flux with wavelength λ3 satisfies the followingexpression.− 1/12<mo<− 1/14  (17)

It is preferable for the optical pickup device described in Item 36 thatthe optical pickup device has a third light source with wavelength λ3(750 nm<λ3<800 nm), the light-converging optical system can conductrecording and/or reproducing of information by converging a divergentlight flux emitted from the third light source on an informationrecording surface of the third optical information recording mediumthrough a t3-thick protective layer, and a diffraction efficiency ofn-th order diffracted light is higher than that of the other orderdiffracted light generated, when the light flux emitted from the thirdlight source passes.

It is preferable for the optical pickup device described in Item 37 thatthe second light source and the third light source are arranged to beequal each other in terms of a distance from the light-convergingoptical element on the optical axis. Incidentally, “being arranged to beequal each other in terms of a distance from the light-convergingoptical element on the optical axis” means a situation wherein thesecond light source and the third light source both representing asemiconductor laser such as, for example, a two-laser in one package,are arranged on the same base board that is perpendicular to the opticalaxis.

It is preferable for the optical pickup device described in Item 38 thatoptical system magnification mo of the light-converging optical elementfor an incident light flux with wavelength λ3 satisfies the followingexpression.− 1/12<mo<− 1/14  (18)

It is possible for the optical pickup device described in Item 39 toconduct recording/reproducing of information appropriately even for thethird optical information recording medium, if the optical pickup devicehas, in the optical path through which a light flux emitted from thethird light source only passes, a coupling lens that changes a divergingangle or a converging angle of a light flux emitted from the third lightsource.

The optical pickup device described in Item 40 is represented by anoptical pickup device that has therein a first light source havingwavelength λ1 (380 nm<λ1<450 nm) and a light-converging optical system,and the light-converging optical system is provided with alight-converging optical element having the diffractive structure and acorrection element arranged between the first light source and thelight-converging optical element, and the light-converging opticalsystem can conduct recording and/or reproducing of information byconverging a light flux emitted from the first light source on aninformation recording surface of the first optical information recordingmedium through a t1-thick protective layer, wherein spherical aberrationdeteriorated by wavelength changes in the first light source andspherical aberration deteriorated by temperature changes are controlledto be in a range necessary for recording and/or reproducing ofinformation on the first spot formed on the information recordingsurface of the first optical information recording medium, thus,recording/reproducing of information can be conducted appropriately forhigh density DVD to take an illustration.

It is preferable for the optical pickup device described in Item 41 thatthe light-converging optical element includes a light-converging opticalelement for converging a light flux emitted from the first light source,a diffractive structure is formed on a part of at least one opticalsurface of the light-converging optical element, and the followingexpression is satisfied when K_(BOL) represents a order of thediffracted light wherein the diffraction efficiency becomes maximum whena light flux emitted from the first light source passes through adiffractive structure of the light-converging optical element, andn_(BOL) represents the number of ring-shaped zones of the diffractivestructure of the light-converging optical element.90<n _(BOL) ·K _(BOL)<130  (19)

It is preferable for the optical pickup device described in Item 42 thata diffractive structure is formed on a part of at least one opticalsurface of the correction element, and the following expression issatisfied when K_(COL) represents a order of the diffracted lightwherein the diffraction efficiency becomes maximum when a light fluxemitted from the first light source passes through a diffractivestructure of the correction element, and n_(COL) represents the numberof ring-shaped zones of the diffractive structure of the correctionelement.30<n _(COL) ·K _(COL)<130  (20)

It is preferable for the optical pickup device described in Item 43 thatchromatic aberration of a light convergence spot caused by changes in alight source wavelength is controlled to be in a range necessary forrecording and/or reproducing of information, on the first spot formed onan information recording surface of the first optical informationrecording medium.

It is preferable for the optical pickup device described in Item 44 thatthe following expression is satisfied by thickness t1 of a protectivelayer of the first optical information recording medium.0.5 mm≦t1≦0.7 mm  (21)

It is preferable for the optical pickup device described in Item 45 thatthe following expression is satisfied by focal length f1 of thelight-converging optical element concerning a light flux emitted fromthe first light source.1.8 mm≦f1≦3.0 mm  (22)

It is preferable for the optical pickup device described in Item 46 thatthe following expression is satisfied by magnification mt of an opticalsystem wherein the light-converging optical element and the correctionelement are combined.−⅓≦mt≦− 1/10  (23)

It is preferable for the optical pickup device described in Item 47 thatcontrolling of spherical aberration deteriorated by fluctuations of thelight source wavelength to be in a range necessary for recording and/orreproducing of information means controlling of an amount of changes inspherical aberration of wavefront aberration to be 0.07 λ rms or lesswhen light source wavelength λ is changed by 10 nm.

It is preferable for the optical pickup device described in Item 48 thatcontrolling of chromatic aberration of a light convergence spot in thecase of a change of a light source wavelength means controlling ofwavefront aberration to 0.02 λ rms or less on the best image positionbefore the change when light source wavelength λ is changed by 1 nm.

It is preferable for the optical pickup device described in Item 49 thatcontrolling of spherical aberration deteriorated by the temperaturechanges to be in a range for recording and/or reproducing of informationmeans controlling of an amount of changes in spherical aberration ofwavefront aberration to 0.04 λ rms or less when the temperature ischanged by 30° C.

It is preferable for the optical pickup device described in Item 50 thatthe following expression is satisfied when NA1 represents a numericalaperture of the light-converging optical element closer to an imagenecessary for conducting recording and/or reproducing of information forthe first optical information recording medium.0.63≦NA1≦0.67  (24)

It is preferable for the optical pickup device described in Item 51 thatthe following expression is satisfied by wavelength fluctuation Δλ/ΔTfor the temperature in the first light source.0.03 nm≦Δλ1/ΔT≦0.1 nm  (25)

The optical pickup device described in Item 52 is characterized to beused in the optical pickup device described in either one of Items 1–51.

The correction element described in Item 53 is characterized to be usedin the optical pickup device described in either one of Items 1–51.

The “diffractive structure” used in the present specification means aportion on the surface of a light-converging optical element or of acorrection element where relief are provided so that the surface mayhave functions to converge or diverge a light flux by diffraction. AS aform of the relief, there is known a shape that is formed, on thesurface of the light-converging optical element or of the correctionelement, as ring-shaped zones which are substantially concentric on theoptical axis and each ring-shaped zone is serrated when its section isobserved on a plane including an optical axis, and the shape of thiskind is included, and this shape is especially called “diffractivering-shaped zones”.

When the diffractive structures are formed on two surfaces or more ofthe light-converging element and the correction element, the number ofdiffractive ring-shaped zones for expressions (3), (4), (5), is the sumtotal of the number of ring-shaped zones of respective surfaces.

In the present specification, the light-converging optical element meansa lens (for example, an objective lens) having light-convergingfunctions arranged at the position closest to an optical informationrecording medium to face it under the state where the opticalinformation recording medium is loaded on the optical pickup device, ina narrow sense, and it means a lens that can be moved together with theaforementioned lens in its optical axis direction by an actuator, in awide sense. Accordingly, in the present specification, numericalaperture NA of the light-converging optical element closer to an opticalinformation recording medium (closer to an image) means numericalaperture NA of the surface of the light-converging optical elementlocated to be closest to the optical information recording medium.Further, in the present specification, necessary numerical aperture NAis assumed to show the numerical aperture stipulated by the standard ofeach optical information recording medium, or a numerical aperture of anobjective lens having diffraction marginal performance which makes itpossible to obtain a spot diameter necessary for recording orreproducing information in accordance with a wavelength of a lightsource to be used.

In the present specification, the first optical information recordingmedium means, for example, an optical disk of a high DVD type, and thesecond optical information recording medium includes optical disks ofvarious DVD types such as DVD-RAM, DVD-R and DVD-RW all serving both asreproducing and recording, in addition to DVD-ROM and DVD-Video bothused exclusively for reproducing. While, the third optical informationrecording medium means an optical disk of a CD type such as CD-R andCD-RW. Further, thickness t of a protective layer in the presentspecification includes also t=0.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of an optical informationrecording and reproducing apparatus or an optical pickup device relatingto the first embodiment for two light sources.

FIG. 2 is a schematic structural diagram of an optical informationrecording and reproducing apparatus or an optical pickup device relatingto the first embodiment for three light sources.

FIG. 3 is a schematic structural diagram of an optical informationrecording and reproducing apparatus or an optical pickup device relatingto the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will be explained as follows in a more detailed way,referring to the drawings. FIG. 1 is a schematic structural diagram ofan optical information recording and reproducing apparatus or an opticalpickup device relating to the first embodiment which can conductrecording/reproducing of information for both high density DVD (which isalso called the first optical disk) and conventional DVD (which is alsocalled the second optical disk). In FIG. 1, a light flux emitted fromfirst semiconductor laser 111 (wavelength λ1=380 nm−450 nm) representingthe first light source is transmitted through ¼ wavelength plate 113 andfirst beam splitter 114, then, is converted by collimator 115representing a correction element into a parallel light flux, andfurther passes second beam splitter 116 to be stopped down by diaphragm17, and is converged by objective lens 16 that serves as alight-converging optical element on information recording surface 22through protective layer 21 (thickness t1=0.5−0.7 mm) of the firstoptical disk 20.

Then, the light flux modulated by information bits and reflected on theinformation recording surface 22 is transmitted through the objectivelens 16 and diaphragm 17 again, then, passes through second beamsplitter 116 and collimator 115 to enter the first beam splitter 114where the light flux is reflected, and is given astigmatism bycylindrical lens 117, and enters photo detector 119 through concave lens118. Thus, reading signals of information recorded on the first opticaldisk 20 are obtained by the use of output signals coming from the photodetector 119.

Changes in an amount of light caused by changes of a form and of aposition of a spot on the photo detector 119 are detected for focusingdetection and track detection. Based on this detection, atwo-dimensional actuator (not shown) moves objective lens 16 so that alight flux emitted from the first semiconductor laser 111 may form animage on recording surface 22 of the first optical disk 20, and movesobjective lens 16 so that a light flux emitted from the semiconductorlaser 111 may form an image on a prescribed track.

On the other hand, a light flux emitted from second semiconductor laser121 (wavelength λ2=600 nm−700 nm) is transmitted through ¼ wavelengthplate 123 and third beam splitter 124, then, is converted by collimator125 representing a correction element into a parallel light flux, andfurther passes through second beam splitter 116 to be stopped down bydiaphragm 17, and is converged by objective lens 16 on informationrecording surface 22 through protective layer 21 (thickness t2=0.5−0.7mm) of the second optical disk 20.

Then, the light flux modulated by information bits and reflected on theinformation recording surface 22 is transmitted through the objectivelens 16 and diaphragm 17 again, then, enters the second beam splitter116 where the light flux is reflected, and passes through collimator 125to enter third beam splitter 124 to be reflected further, and is givenastigmatism by cylindrical lens 127, and enters photo detector 129through concave lens 128. Thus, reading signals of information recordedon the second optical disk 20 are obtained by the use of output signalscoming from the photo detector 129.

Changes in an amount of light caused by changes of a form and of aposition of a spot on the photo detector 129 are detected for focusingdetection and track detection. Based on this detection, atwo-dimensional actuator (not shown) moves objective lens 16 so that alight flux emitted from the second semiconductor laser 121 may form animage on recording surface 22 of the second optical disk 20, and movesobjective lens 16 so that a light flux emitted from the semiconductorlaser 121 may form an image on a prescribed track.

Incidentally, though collimators 115 and 125 are provided respectivelyin an optical path between the first semiconductor laser 111 andobjective lens 16 and in an optical path between the secondsemiconductor laser 121 and objective lens 16, in FIG. 1, it is alsopossible to provide a collimator equipped with a correction function ineither one of the optical paths. The example which will be explainedlater corresponds to an occasion wherein collimator 125 (for DVD) onlyhas a correction function, and interchangeability for high density DVD,DVD and CD is given (which means that recording/reproducing ofinformation is made to be capable of being conducted for any one of theaforementioned optical information recording media, and so on) (Example1), an occasion wherein collimator 115 (for high density DVD) only has acorrection function, and interchangeability for high density DVD and DVDis given (Example 2), or an occasion wherein interchangeability for highdensity DVD, DVD and CD is given (Examples 3, 4 and 5). Incidentally, inthe case of Examples 1, 3, 4 and 5, a light source and an optical pathfor the third optical information recording medium (CD in this case) areomitted in FIG. 1. In these cases, it is also possible to employ for theoptical pickup device wherein recording/reproducing of information isnot conducted for the third optical information recording medium andinterchangeability is given to high density DVD and DVD.

FIG. 2 is a schematic structural diagram of an optical informationrecording and reproducing apparatus or an optical pickup device relatingto the first embodiment for three light sources.

In FIG. 2, in addition to the structure of FIG. 1, the thirdsemiconductor laser 131 (wavelength λ3=750 nm−800 nm), the photodetector 139, the diffractive optical element 133 and the coupling lens134 are added for CD provided with a protective layer (thickness t3=1.2mm).

FIG. 3 is a schematic structural diagram of an optical informationrecording and reproducing apparatus or an optical pickup device relatingto the second embodiment which can conduct recording/reproducing ofinformation for only high density DVD. In FIG. 3, a light flux emittedfrom first semiconductor laser 111 (wavelength λ1=380 nm−450 nm)representing the first light source is transmitted through ¼ wavelengthplate 113 and beam splitter 114, then, is converted by collimator 115representing a correction element into a parallel light flux, andfurther stopped down by diaphragm 17, and is converged by objective lens16 that serves as a light-converging optical element on informationrecording surface 22 through protective layer 21 (thickness t1=0.5−0.7mm) of the first optical disk 20.

Then, the light flux modulated by information bits and reflected on theinformation recording surface 22 is transmitted through the objectivelens 16 and diaphragm 17 again and passes through collimator 115, then,enters beam splitter 114 where the light flux is reflected, and is givenastigmatism by cylindrical lens 117, and enters photo detector 119through concave lens 118. Thus, reading signals of information recordedon the first optical disk 20 are obtained by the use of output signalscoming from the photo detector 119.

Changes in an amount of light caused by changes of a form and of aposition of a spot on the photo detector 119 are detected for focusingdetection and track detection. Based on this detection, atwo-dimensional actuator (not shown) moves objective lens 16 so that alight flux emitted from the first semiconductor laser 111 may form animage on recording surface 22 of the first optical disk 20, and movesobjective lens 16 so that a light flux emitted from the semiconductorlaser 111 may form an image on a prescribed track.

An example that is preferable for the aforementioned embodiment will beexplained as follows.

Each of both sides of the objective lens is an aspheric surfaceexpressed by “Numeral 1”. Z represents an axis in the direction of anoptical axis, h represents a height from the optical axis, r representsa paraxial radius of curvature, κ represents a constant of the cone andA_(2i) represents an aspheric surface coefficient.

$\begin{matrix}{Z = {\frac{\left( {h^{2}/r} \right)}{1 + \sqrt{1 - {\left( {1 + \kappa} \right)\left( {h/r} \right)^{2}}}} + {\sum\limits_{i = 1}^{9}\;{A_{i}h^{Pi}}}}} & \left( {{Numeral}\mspace{14mu} 1} \right)\end{matrix}$

Further, a diffractive structure is formed solidly on the surface of anaspheric surface of the objective lens closer to a light source. Thisdiffractive structure is expressed by optical path difference function Φfor blazed wavelength in “Numeral 2” with a unit of mm. The secondarycoefficient expresses paraxial power of the diffracting portion.Spherical aberration can be controlled by the coefficient of the orderother than the secondary order, such as, for example, the fourth ordercoefficient or the sixth order coefficient. “Spherical aberration can becontrolled” means that the spherical aberration owned by the refractionportion is corrected as a total by giving spherical aberration havingopposite characteristics to the diffraction portion and sphericalaberration is corrected or a flare is made to be caused by a wavelengthof incident light by utilizing wavelength-dependency of the diffractionportion. In this case, spherical aberration caused by changes intemperatures is also considered to be the total of the temperaturechanges of spherical aberration of the refraction portion and sphericalaberration of the diffraction portion.

$\begin{matrix}{\Phi = {\sum\limits_{i = 1}^{\infty}\;{{c2i}\mspace{31mu} h^{2i}\mspace{14mu}({mm})}}} & \left( {{Numeral}\mspace{14mu} 2} \right)\end{matrix}$

EXAMPLE 1

The present example is one which is appropriate when collimator 125representing a correction element is provided only in an optical pathbetween the second semiconductor laser 121 and objective lens 16 inFIGS. 1 and 2 (namely, collimator 115 has no correction functions). Lensdata of the optical system (objective lens+collimator) relating to thepresent example are shown in Tables 1 and 2. In the objective lens 16, adiffractive structure is provided on the area (that is called a commonarea) through which the first semiconductor laser 111 and the secondsemiconductor laser 121 pass and the diffractive structure is providedalso on the collimator 125, which is clear from Tables 1 and 2.Incidentally, hereafter (including lens data in the Tables), a powermultiplier of 10 (for example, 2.5×10⁻³) is assumed to be expressed byusing E (for example, 2.5×E-3).

TABLE 1 Example 1 Lens data Focal length of objective lens f₁ = 2.4 mmf₂ = 2.46 mm f₃ = 2.49 mm Numerical aperture on the NA1:0.65 NA2:0.65NA3:0.45 image surface side i-th surface ri di (407 nm) ni (407 nm) di(655 nm) ni (655 nm) di (785 nm) ni (785 nm) 0 ∞ 12.75 33.74 1 −8.677511.5 1.540513 2 −3.85279 5 1.0 3 *1 ∞ 0.1 0.1 0.1 (φ3.120mm) (φ3.192mm)(φ2.401mm) 4  1.59131 1.60000 1.524609 1.60000 1.506732 1.60000 1.5034534′  2.16692 0.15126 1.524609 0.15126 1.506732 0.15126 1.503453 5−5.85891 1.12 1.0 1.16 1.0 1.01 1.0 5′ −5.51220 0.00000 1.0 0.00000 1.00.00000 1.0 6 ∞ 0.6 1.61869 0.6 1.57752 1.2 1.57063 7 ∞ *1; (Diaphragmdiameter) * The symbol di shows a displacement from the i-th surface to(i + 1)th surface. * The symbol d4′ shows a displacement from the fourthsurface to the 4′th surface, and the symbol d5′ shows a displacementfrom the fifth surface to the 5′th surface.

TABLE 2 Aspheric surface data First surface (for DVD only) Aspheric κ−2.7276 × E − 0 surface A1 −4.5283 × E − 4 P1 4.0 coefficient A2 +1.3214× E − 4 P2 6.0 Optical C2 +1.6614 × E + 1 path C4 +3.3501 × E − 0difference C6 +1.5629 × E − 0 function C8 +3.2769 × E − 2 C10 −2.7011 ×E − 2 Second surface (for DVD only) Aspheric κ −0.1000 × E − 0 surfaceA1 −1.4368 × E − 3 P1 4.0 coefficient A2 −8.1143 × E − 4 P2 6.0 Fourthsurface (0 <h <1.56 mm: HD-DVD/DVD common area) Aspheric κ −7.4653 × E −1 surface A1 +8.3080 × E − 3 P1 4.0 coefficient A2 −8.7702 × E − 4 P26.0 A3 +1.3463 × E − 3 P3 8.0 A4 −7.9116 × E − 4 P4 10.0 A5 +2.9845 × E− 4 P5 12.0 A6 −6.6527 × E − 5 P6 14.0 Optical C2 −1.2851 × E − 1 pathC4 −1.8026 × E − 0 difference C6 −1.1807 × E − 2 function C8 −1.0354 × E− 1 C10 +4.8953 × E − 3 4′th surface(1.56 mm ≦ h: area for DVD only)Aspheric κ −7.4653 × E − 1 surface A1 −8.3080 × E − 3 P1 4.0 coefficientA2 −8.7702 × E − 4 P2 6.0 A3 +1.3463 × E − 3 P3 8.0 A4 −7.9116 × E − 4P4 10.0 A5 +2.9845 × E − 4 P5 12.0 A6 −6.6527 × E − 4 P6 14.0 Optical C2−4.0492 × E + 1 path C4 +1.2757 × E − 0 difference C6 +2.8435 × E − 0function C8 +1.0392 × E − 0 C10 −9.0342 × E − 1 Fifth surface (0 < h <1.287 mm) Aspheric κ −9.6287 × E + 1 surface A1 −3.4537 × E − 2 P1 4.0coefficient A2 +1.2630 × E − 2 P2 6.0 A3 −9.0327 × E − 3 P3 8.0 A4+2.2022 × E − 3 P4 10.0 A5 −1.0621 × E − 4 P5 12.0 A6 −3.1979 × E − 5 P614.0 5′th surface (1.287 mm ≦ h) Aspheric κ −1.5903 × E + 2 surface A1+8.4430 × E − 4 P1 4.0 coefficient A2 +1.2839 × E − 2 P2 6.0 A3 −9.6961× E − 3 P3 8.0 A4 +1.9433 × E − 3 P4 10.0 A5 −8.6437 × E − 5 P5 12.0 A6−1.8294 × E − 5 P6 14.0

Specifications of the present example are as follows.

-   -   (1) Number of diffractive ring-shaped zones (primary        diffraction) for objective lens common area N1: 23    -   (2) Number of ring-shaped zones for collimator (secondary        diffraction) N2: 18    -   (3) Magnification of optical system on the part of high density        DVD (first optical disk) mo: −⅙    -   (4) Protective layer thickness t1, t2: 0.6 mm, t3: 1.2 mm    -   (5) Order of diffracted light by maximum diffraction efficiency        by diffractive structure of objective lens common area

High density DVD: conventional DVD: CD=6:4:3

-   -   (6) Optical system magnification of objective lens for light        having each wavelength

High density DVD: conventional DVD: CD=0:0:− 1/12.7

Incidentally, the light-converging optical system of the present exampleis appropriate when it is used for the optical pickup devices in Items 4and 32.

EXAMPLES 2–5

Each of the present examples 2–5 is one which is appropriate whencollimator 115 representing a correction element is provided only in anoptical path between the first semiconductor laser 111 and objectivelens 16 in FIGS. 1 and 2 (namely, collimator 125 has no correctionfunctions).

EXAMPLE 2

Lens data of the light-converging optical system relating to Example 2(objective lens+collimator) are shown in Tables 3 and 4.

TABLE 3 Example 2 Lens data Focal length of objective lens f₁ = 2.4 mmf₂ = 2.46 mm Numerical aperture on the NA1:0.65 NA2:0.65 image surfaceside i-th surface ri di (407 nm) ni (407 nm) di (655 nm) ni (655 nm) 012.79 ∞ 1 −8.3107 1.5 1.542771 2 −4.7378 5.1 1.0 3 ∞ 0.0 1.0 0.0 1.0Diaphragm diameter φ3.192 mm 4  1.54227 1.60000 1.542771 1.60000 1.529154′  2.09495 0.15126 1.542771 0.15126 1.52915 5 −5.85469 1.14000 1.01.07000 1.0 6 ∞ 0.6 1.61869 0.6 1.57752 7 ∞ * The symbol di shows adisplacement from the i-th surface to (i + 1)th surface. The symbol d4′shows a displacement from the fourth surface to 4′th surface.

TABLE 4 Aspheric surface data First surface (for HD-DVD only) Aspheric κ+3.5236 × E − 0 surface A1 −7.4347 × E − 4 P1 4.0 coefficient A2 −1.1113× E − 3 P2 6.0 Optical C2 −1.7730 × E + 1 path C4 +1.6436 × E − 0difference C6 −1.2341 × E − 0 function C8 +5.5958 × E − 2 C10 +5.8919 ×E − 2 Second surface (for HD-DVD only) Aspheric κ +2.9191 × E − 0surface A1 +2.1252 × E − 3 P1 4.0 coefficient A2 +3.1469 × E − 4 P2 6.0Fourth surface (0 < h < 1.56 mm: HD-DVD/DVD common area) Aspheric κ−7.6953 × E − 1 surface A1 +8.4000 × E − 3 P1 4.0 coefficient A2 −9.2000× E − 4 P2 6.0 A3 +1.6657 × E − 3 P3 8.0 A4 −7.3116 × E − 4 P4 10.0 A5+2.3051 × E − 4 P5 12.0 A6 −5.7188 × E − 5 P6 14.0 Optical C2 −2.6573 ×E − 0 path C4 −1.0803 × E − 0 difference C6 −2.5559 × E − 1 function C8+8.6007 × E − 2 C10 −2.9751 × E − 2 4′th surface (1.56 mm ≦ h: area forDVD only) Aspheric κ −4.0617 × E − 0 surface A1 −5.2846 × E − 3 P1 4.0coefficient A2 +6.8538 × E − 3 P2 6.0 A3 +2.5685 × E − 2 P3 8.0 A4+7.6026 × E − 3 P4 10.0 A5 −5.6376 × E − 4 P5 12.0 A6 +1.9688 × E − 4 P614.0 Optical C2 −3.5650 × E + 1 path C4 +6.2611 × E − 0 difference C6+3.8905 × E − 0 function C8 +1.1623 × E − 0 C10 −9.3398 × E − 1 Fifthsurface Aspheric κ −7.5809 × E + 1 surface A1 −2.8052 × E − 3 P1 4.0coefficient A2 +1.3670 × E − 2 P2 6.0 A3 −9.5656 × E − 3 P3 8.0 A4+1.7676 × E − 3 P4 10.0 A5 +2.9457 × E − 4 P5 12.0 A6 −1.1557 × E − 4 P614.0

Specifications of the present example are as follows.

-   -   (7) (1) Number of diffractive ring-shaped zones (primary        diffraction) for objective lens common area N1: 16    -   (8) (2) Number of ring-shaped zones for collimator (secondary        diffraction) N2: 18    -   (9) (3) Magnification of optical system on the part of high        density DVD (first optical disk) mo: −⅙    -   (10) (4) Protective layer thickness t1, t2: 0.6 mm    -   (11) (5) Order of diffracted light by maximum diffraction        efficiency by diffractive structure of objective lens common        area

High density DVD: conventional DVD=3:2

-   -   (12) (6) Optical system magnification of objective lens for        light having each wavelength

High density DVD: conventional DVD=0:0

Incidentally, the light-converging optical system of the present exampleis appropriate when it is used for the optical pickup devices in Items 4and 12.

EXAMPLE 3

The present example is also appropriate for the optical pickup deviceshown in FIG. 3. Lens data of the light-converging optical systemrelating to the present example (objective lens+collimator) are shown inTable 5.

TABLE 5 Example 3 Lens data Focal length of objective lens f₁ = 2.4 mmf₂ = 2.4 mm f₃ = 2.5 mm Numerical aperture on the NA1:0.65 NA2:0.65NA2:0.45 image surface side i-th surface ri di (407 nm) ni (407 nm) di(655 nm) ni (655 nm) di (785 nm) ni (785 nm) 0 14.15 12.65 35.30 137.65302 1.50 1.542771 2 −3.06488 5.00 1.00 3 *1 ∞ 0.1 0.1 0.1 (φ3.120mm) (φ3.123 mm) (φ2.405 mm) 4 1.94029 1.60 1.524609 1.60 1.506732 1.601.503453 5 −19.05844 1.02 1.0 1.00 1.0 0.90 1.0 6 ∞ 0.60 1.61869 0.601.57752 1.20 1.57063 7 ∞ *1; (Diaphragm diameter) * The symbol di showsa displacement from the i-th surface to (i + 1)th surface.

Aspheric surface data First surface (for HD-DVD only) Aspheric κ −2.0527× E − 1 surface A1 +1.2177 × E − 2 P1 4.0 coefficient A2 −1.4613 × E − 4P2 6.0 Second surface (for HD-DVD only) Aspheric κ −1.0874 × E − 1surface A1 +9.5823 × E − 3 P1 4.0 coefficient A2 +7.0554 × E − 4 P2 6.0Optical path C2 +1.4605 × E + 2 difference C4 +5.9202 × E − 0 functionC6 +3.1566 × E − 0 Fourth surface Aspheric κ −7.6390 × E − 1 surface A1+5.7888 × E − 3 P1 4.0 coefficient A2 +5.9520 × E − 4 P2 6.0 A3 +9.0951× E − 4 P3 8.0 A4 −9.9238 × E − 4 P4 10.0 A5 +4.0468 × E − 4 P5 12.0 A6−7.5725 × E − 5 P6 14.0 Optical path C2 −2.6687 × E + 1 difference C4−1.6322 × E − 0 function C6 +5.5099 × E − 2 C8 −1.0644 × E − 0 C10+1.3015 × E − 2 Fifth surface Aspheric κ −4.5835 × E + 2 surface A1+1.8084 × E − 2 P1 4.0 coefficient A2 −4.3442 × E − 3 P2 6.0 A3 −4.5714× E − 3 P3 8.0 A4 +4.1244 × E − 3 P4 10.0 A5 −2.4595 × E − 3 P5 12.0 A6+5.7937 × E − 4 P6 14.0

Specifications of the present example are as follows.

-   -   (13) (1) Number of diffractive ring-shaped zones (primary        diffraction) for objective lens common area N1: 81    -   (14) (2) Number of ring-shaped zones for collimator (primary        diffraction) N2: 366    -   (15) (3) Magnification of optical system on the part of the        first optical disk mo: −⅙    -   (16) (4) Protective layer thickness t1, t2: 0.6 mm, t: 1.2 mm    -   (17) (5) Order of diffracted light by maximum diffraction        efficiency by diffractive structure of objective lens common        area

High density DVD: conventional DVD: CD=6:4:3

-   -   (18) (6) Optical system magnification of objective lens for        light having each wavelength

High density DVD: conventional DVD: CD=0:0:− 1/13.2

Incidentally, the light-converging optical system of the present exampleis appropriate when it is used for the optical pickup devices in Items 4and 32.

EXAMPLE 4

The present example is appropriate for the optical pickup device shownin FIG. 3. Lens data of the light-converging optical system relating tothe present example (objective lens+collimator) are shown in Table 6.

TABLE 6 Example 4 Lens data Focal length of objective lens f₁ = 2.4 mmf₂ = 2.45 mm f₃ = 2.50 mm Numerical aperture on the NA1:0.65 NA2:0.65NA2:0.45 image surface side i-th surface ri di (407 nm) ni (407 nm) di(655 nm) ni (655 nm) di (785 nm) ni (785 nm) 0 14.15 827.00 36.16 137.65302 1.50 1.542771 2 −3.06488 5.00 1.00 3 *1 ∞ 0.1 0.1 0.1 (φ3.120mm) (φ3.198 mm) (φ2.403 mm) 4 1.92291 1.60 1.524609 1.60 1.506732 1.601.503453 5 −19.08099 1.02 1.0 1.06 1.0 0.89 1.0 6 ∞ 0.60 1.61869 0.601.57752 1.20 1.57063 7 ∞ *1; (Diaphragm diameter) * The symbol di showsa displacement from the i-th surface to (i + 1)th surface.

Aspheric surface data First surface (for HD-DVD only) Aspheric κ −2.0527× E − 1 surface A1 +1.2177 × E − 2 P1 4.0 coefficient A2 −1.4613 × E − 4P2 6.0 Second surface (for HD-DVD only) Aspheric κ −1.0874 × E − 1surface A1 +9.5823 × E − 3 P1 4.0 coefficient A2 +7.0554 × E − 4 P2 6.0Optical path C2 +1.4605 × E + 2 difference C4 +5.9202 × E − 0 functionC6 +3.1566 × E − 0 Fourth surface Aspheric κ −7.9792 × E − 1 surface A1+4.9330 × E − 3 P1 4.0 coefficient A2 +7.0747 × E − 4 P2 6.0 A3 +9.4490× E − 4 P3 8.0 A4 −1.0691 × E − 3 P4 10.0 A5 +4.1435 × E − 4 P5 12.0 A6−7.3960 × E − 5 P6 14.0 Optical path C2 −1.9643 × E + 1 difference C4−1.5085 × E − 0 function C6 +1.0855 × E − 1 C8 −1.0372 × E − 1 C10+1.3735 × E − 2 Fifth surface Aspheric κ −5.2563 × E + 2 surface A1+1.7853 × E − 2 P1 4.0 coefficient A2 −4.7662 × E − 3 P2 6.0 A3 −4.9002× E − 3 P3 8.0 A4 +4.0691 × E − 3 P4 10.0 A5 −1.9875 × E − 3 P5 12.0 A6+3.9475 × E − 4 P6 14.0

Specifications of the present example are as follows.

-   -   (19) (1) Number of diffractive ring-shaped zones (primary        diffraction) for objective lens common area N1: 81    -   (20) (2) Number of ring-shaped zones for collimator (primary        diffraction) N2: 1    -   (21) (3) Magnification of optical system on the part of the        first optical disk mo: −⅙    -   (22) (4) Protective layer thickness t1, t2: 0.6 mm, t3: 1.2 mm    -   (23) (5) Order of diffracted light by maximum diffraction        efficiency by diffractive structure of objective lens common        area

High density DVD: conventional DVD: CD=2:1:1

-   -   (24) (6) Optical system magnification of objective lens for        light having each wavelength

High density DVD: conventional DVD: CD=0:− 1/13.1:− 1/13.0

Incidentally, the light-converging optical system of the present exampleis appropriate when it is used for the optical pickup devices in Items 3and 36.

EXAMPLE 5

The light-converging optical system of the present example isappropriate for the optical pickup devices of Items 5 and 34. Lens dataof the light-converging optical system relating to the present example(objective lens+collimator) are shown in Table 7.

TABLE 7 Example 5 Lens data Focal length of objective lens f₁ = 2.4 mmf₂ = 2.4 mm f₃ = 2.49 mm Numerical aperture on the NA1:0.65 NA2:0.65NA2:0.45 image surface side i-th surface ri di (407 nm) ni (407 nm) di(655 nm) ni (655 nm) di (785 nm) ni (785 nm) 0 13.45 12.75 34.74 11643.88 1.50 1.542771 2 −9.1285 5.10 1.0 3 *1 ∞ 0.1 0.1 0.1 (φ3.120 mm)(φ3.452 mm) (φ2.392 mm) 4 1.54056 1.70 1.524609 1.70 1.506732 1.701.503453 5 −5.05826 1.08 1.0 1.35 1.0 1.35 1.0 6 ∞ 0.60 1.61869 0.601.57752 1.20 1.57063 7 ∞ *1; (Diaphragm diameter) * The symbol di showsa displacement from the i-th surface to (i + 1)th surface.

Aspheric surface data First surface (for HD-DVD only) Aspheric κ −2.0527× E − 33 surface A1 +6.1818 × E − 3 P1 4.0 coefficient A2 −1.7991 × E −3 P2 6.0 Second surface (for HD-DVD only) Aspheric κ +7.8948 × E − 0surface A1 +5.2959 × E − 3 P1 4.0 coefficient A2 −2.3710 × E − 3 P2 6.0Optical path C2 −1.3131 × E + 1 difference C4 +1.4411 × E − 0 functionC6 +1.7083 × E − 0 Fourth surface Aspheric κ −7.7790 × E − 1 surface A1+5.1727 × E − 3 P1 4.0 coefficient A2 +1.1101 × E − 3 P2 6.0 A3 −6.4972× E − 4 P3 8.0 A4 −5.9817 × E − 4 P4 10.0 A5 +3.3629 × E − 4 P5 12.0 A6−6.2531 × E − 5 P6 14.0 Optical path C2 −8.1974 × E + 0 difference C4−5.7385 × E − 0 function C6 +1.8525 × E − 0 C8 −1.7519 × E − 0 C10+3.7926 × E − 1 Fifth surface Aspheric κ −6.6494 × E + 1 surface A1+4.7077 × E − 3 P1 4.0 coefficient A2 +1.8991 × E − 3 P2 6.0 A3 −4.8520× E − 3 P3 8.0 A4 +1.6255 × E − 3 P4 10.0 A5 −2.4962 × E − 4 P5 12.0 A6+1.1626 × E − 5 P6 14.0

-   -   (26) (2) Number of ring-shaped zones for collimator (secondary        diffraction) N2: 377    -   (27) (3) Magnification of optical system on the part of high        density DVD (first optical disk) m: −⅙    -   (28) (4) Protective layer thickness t1, t2: 0.6 mm, t3: 1.2 mm    -   (29) (5) Order of diffracted light by maximum diffraction        efficiency by diffractive structure of objective lens common        area

High density DVD: conventional DVD: CD=8:5:4

-   -   (30) (6) Optical system magnification of objective lens for        light having each wavelength

High density DVD: conventional DVD: CD=0:− 1/333:− 1/13.4

EXAMPLE 6

Lens data of the objective lens of the light-converging optical systemrelating to Example 6 are shown in Table 8, and lens data of thecollimator of the light-converging optical system relating to Example 6are shown in Table 9. Incidentally, the light-converging optical systemin Example 6 and in Example 7 which will be described later is one thatcan be used in the optical pickup device shown in FIG. 3.

TABLE 8 Example 6 Lens data Objective lens 1 f1 = 2.4 mm NA: 0.65

i-th surface ri di ni (405 nm) 0 ∞ 1 ∞ 0.0 1.0 Diaphragm diameter φ3.22mm 2  1.45460 1.50000 1.52461 3 −6.04260 1.17774 1.0 4 ∞ 0.6 1.62 5 ∞*The symbol di shows a displacement from the i-th surface to (i + 1)thsurface.

Aspheric surface data Second surface Aspheric κ −1.9937 × E − 0 surfaceA1 +1.6862 × E − 2 P1 4.0 coefficient A2 +2.4659 × E − 2 P2 6.0 A3−8.4628 × E − 3 P3 8.0 A4 −2.6596 × E − 4 P4 10.0 A5 +2.7611 × E − 4 P512.0 A6 −3.5091 × E − 5 P6 14.0 *1 C4 −5.6672 × E + 1 C6 +4.5666 × E + 1C8 −1.8280 × E + 1 C10 +2.5654 × E − 0 Third surface Aspheric κ +5.0000× E + 1 surface A1 +1.0025 × E − 2 P1 4.0 coefficient A2 +4.2022 × E − 3P2 6.0 A3 −6.3019 × E − 3 P3 8.0 A4 +2.5320 × E − 3 P4 10.0 A5 −5.4683 ×E − 4 P5 12.0 A6 +5.2137 × E − 5 P6 14.0 *1; Optical path differencefunction (Coefficient of optical path difference function: Standardwavelength 1 mm)

TABLE 9 (Collimator 1 for Example 6 Lens data Objective lens 1) f1 =14.4 mm

i-th surface ri di ni (405 nm) 0 ∞ 1 ∞ 0.0 1.0 Diaphragm diameter φ3.22mm 2  5.42216 1.50000 1.52461 3 11.0102  13.0275 1.0 4 ∞ 1.0 *The symboldi shows a displacement from the i-th surface to (i + 1)th surface.

Aspheric surface data Second surface Aspheric κ +4.5254 × E − 0 surfaceA1 −2.0556 × E − 3 P1 4.0 coefficient A2 −8.4275 × E − 4 P2 6.0 Thirdsurface *1 C2 −2.1495 × E + 1 C4 +1.4345 × E − 0 C6 −1.1092 × E − 0 C8−1.1630 × E − 1 C10 +4.7356 × E − 2 *1; Optical path difference function(Coefficient of optical path difference function: Standard wavelength 1mm)

Specifications of the present example are as follows.

-   -   (31) (1) Number of diffractive ring-shaped zones of objective        lens (primary diffraction) N1: 100    -   (32) (2) Number of ring-shaped zones for collimator (primary        diffraction) N2: 48    -   (33) (3) Magnification of optical system of combination of        collimator and objective mt: −⅙    -   (34) (4) Protective layer thickness: 0.6 mm

EXAMPLE 7

Lens data of the collimator of the light-converging optical systemrelating to Example 7 are shown in Table 10. Incidentally, the objectivelens in Example 6 shown in Table 8 can be used as the objective lensused together with the collimator in Example 7.

TABLE 10 (Collimator 2 for Example 7 Lens data Objective lens 1) f1 =14.4 mm

i-th surface ri di ni (405 nm) 0 ∞ 1 ∞ 0.0 1.0 Diaphragm diameter φ3.22mm 2  5.37212 1.50000 1.52461 3 11.2778  12.8918 1.0 4 ∞ 1.0 * Thesymbol di shows a displacement from the i-th surface to (i + 1)thsurface.

Aspheric surface data Second surface Aspheric κ +4.3443 × E − 0 surfaceA1 −2.3164 × E − 3 P1 4.0 coefficient A2 −1.1874 × E − 3 P2 6.0 Thirdsurface *1 C2 −1.8815 × E + 1 C4 +2.8757 × E − 0 C6 −1.8681 × E − 0 C8−1.2050 × E − 1 C10 +4.5833 × E − 2 *1; Optical path difference function(Coefficient of optical path difference function: Standard wavelength 1mm)

Specifications of the present example are as follows.

-   -   (35) (1) Number of diffractive ring-shaped zones of objective        lens (primary diffraction) N1: 100    -   (36) (2) Number of ring-shaped zones for collimator (primary        diffraction) N2: 39    -   (37) (3) Magnification of optical system of combination of        collimator and objective mt: −⅙    -   (38) (4) Protective layer thickness: 0.6 mm

The respective wavefront aberrations of the Examples 1–7 stated aboveproved to be excellent as shown in Table 11.

TABLE 11 First optical Second optical [λ] disk disk Example 1 (1) 0.0180.003 (2) 0.038 0.008 (3) 0.028 0.017 Example 2 (1) 0.013 0.002 (2)0.036 0.022 (3) 0.024 0.010 Example 3 (1) 0.010 0.128 (2) 0.034 0.010(3) 0.005 0.004 Example 4 (1) 0.008 0.022 (2) 0.038 0.050 (3) 0.0230.045 Example 5 (1) 0.012 0.127 (2) 0.056 0.016 (3) 0.013 0.005 Example6 (1) 0.004 (2) 0.047 (3) 0.022 Example 7 (1) 0.006 (2) 0.065 (3) 0.012Characteristics of Each Number

-   (1) Amount of changes in wavefront aberration for wavelength change    Δλ=+1 nm, at the best image surface position under the standard    condition-   (2) Amount of changes in wavefront aberration for wavelength change    Δλ=+10 nm, at the best image surface position-   (3) Amount of changes in wavefront aberration at the best image    surface position for temperature change ΔT=30° C.    (Effect of the Invention)

The invention makes it possible to provide an optical pickup device thatis of a compact structure and yet is capable of conducting recording andreproducing for information properly for high density DVD or for bothhigh density DVD and conventional DVD, and to provide an optical systemthat can be used for the optical pickup device.

1. An optical pickup device, comprising: a first light source to emit afirst light flux having a wavelength λ1 (380 nm<λ1<450 nm); a secondlight source to emit a second light flux having a wavelength λ2 (600nm<λ2<700 nm); and a light-converging optical system having alight-converging optical element including a diffractive structure and acorrecting element arranged between the first light source and/or thesecond light source and the light-converging optical element; whereinthe light-converging optical system converges the first light fluxemitted from the first light source on an information recording surfaceof a first optical information recording medium through a protectivelayer having a thickness t1 so that the optical pickup device conductsrecording and/or reproducing information for the first informationrecording medium and the light-converging optical system converges thesecond light flux emitted from the second light source on an informationrecording surface of a second optical information recording mediumthrough a protective layer having a thickness t2 so that the opticalpickup device conducts recording and/or reproducing information for thesecond information recording medium, wherein the light-convergingoptical system forms a first spot on the information recording surfaceof the first optical information recording medium by using N-th orderdiffracted light ray generated when the first light flux from the firstlight source passes through the diffractive structure of thelight-converging optical system, and the light-converging optical systemforms a second spot on the information recording surface of the secondoptical information recording medium by using M-th order (M≠N)diffracted light ray generated when the second light flux from thesecond light source passes through the diffractive structure of thelight-converging optical system, and wherein on the first spot formed onthe information recording surface of the first optical informationrecording medium, a deteriorated spherical aberration due to awavelength change in the first light source and a deteriorated sphericalaberration due to a temperature change are regulated to be within arange necessary for recording and/or reproducing of information, and onthe second spot formed on the information recording surface of thesecond optical information recording medium, a deteriorated sphericalaberration due to a wavelength change in the second light source and adeteriorated spherical aberration due to a temperature change areregulated to be within a range necessary for recording and/orreproducing of information.
 2. The optical pickup device of claim 1,wherein on the first spot formed on an information recording surface ofthe first optical information recording medium, a chromatic aberrationof the converged spot caused by a change in a wavelength of a lightsource is regulated to be within a range necessary for recordingand/reproducing of information, and on the second spot formed on aninformation recording surface of the second optical informationrecording medium, a chromatic aberration of the converged spot caused bya change in a wavelength of a light source is regulated to be within arange necessary for recording and/reproducing of information.
 3. Theoptical pickup device of claim 1, wherein t1 representing a thickness ofa protective layer of the first optical information recording medium andt2 representing a thickness of a protective layer of the second opticalinformation recording medium satisfy the following expressions:0.5 mm≦t1≦0.7 mm0.5 mm≦t2≦0.7 mm.
 4. The optical pickup device of claim 1, wherein thediffractive structure is provided on a area on a part of at least oneoptical surface of the light converging optical element through whichboth of the first and second light fluxes commonly pass when conductingrecording and/or reproducing of information for the first and secondoptical information recording mediums, a diffraction efficiency of 3m-th(m represents a positive integer) order diffracted light ray becomeshigher than a diffraction efficiency of any one of other orderdiffracted light rays generated when the first light flux emitted fromthe first light source passes through the diffractive structure, and adiffraction efficiency of 2m-th order diffracted light becomes higherthan a diffraction efficiency of any one of other order diffracted lightrays generated when the second light flux emitted from the second lightsource passes through the diffractive structure.
 5. The optical pickupdevice of claim 1, wherein the diffractive structure is provided on aarea on a part of at least one optical surface of the light convergingoptical element through which both of the first and second light fluxescommonly pass when conducting recording and/or reproducing ofinformation for the first and second optical information recordingmediums, a diffraction efficiency of 8p-th (p represents a positiveinteger) order diffracted light ray becomes higher than a diffractionefficiency of any one of other order diffracted light rays generatedwhen the first light flux emitted from the first light source passesthrough the diffractive structure, and a diffraction efficiency of 5p-thorder diffracted light becomes higher than a diffraction efficiency ofany one of other order diffracted light rays generated when the secondlight flux emitted from the second light source passes through thediffractive structure.
 6. The optical pickup device of claim 1, whereinthe diffractive structure is provided on a area on a part of at leastone optical surface of the light converging optical element throughwhich both of the first and second light fluxes commonly pass whenconducting recording and/or reproducing of information for the first andsecond optical information recording mediums, a diffraction efficiencyof 2n-th (n represents a positive integer) order diffracted light raybecomes higher than a diffraction efficiency of any one of other orderdiffracted light rays generated when the first light flux emitted fromthe first light source passes through the diffractive structure, and adiffraction efficiency of n-th order diffracted light becomes higherthan a diffraction efficiency of any one of other order diffracted lightrays generated when the second light flux emitted from the second lightsource passes through the diffractive structure.
 7. The optical pickupdevice of claim 1, wherein the correcting element is arranged in anoptical path through which only the first light flux emitted from thefirst light source passes, or arranged in an optical path through whichonly the second light flux emitted from the second light source passes.8. The optical pickup device of claim 7, wherein the correcting elementis arranged in an optical path through which only the second light fluxemitted from the second light source passes, and wherein on the firstspot formed on an information recording surface of the first opticalinformation recording medium, a chromatic aberration of the convergedspot caused by a change in a wavelength of a light source is regulatedby the light converging optical element so as to be within a rangenecessary for recording and/reproducing of information, and on thesecond spot formed on an information recording surface of the secondoptical information recording medium, a chromatic aberration of theconverged spot caused by a change in a wavelength of a light source isregulated by the correcting element so as to be within a range necessaryfor recording and/reproducing of information.
 9. The optical pickupdevice of claim 8, wherein on the diffractive structure provided on thelight-converging optical element, the number N1 of diffractivering-shaped zones existing on the area where both of the first andsecond light fluxes commonly pass when conducting recording and/orreproducing of information for the first and second optical informationrecording mediums satisfies the following formula;115/A≦N1≦155/A where A is 3m or 8p and is a order of diffracted lightray whose diffraction efficiency is higher than that of any one of otherorder diffracted light rays of the first light flux having a wavelengthλ1.
 10. The optical pickup device of claim 8, wherein the correctingelement comprises a diffractive structure on at least one opticalsurface thereof and the number N2 of diffractive ring-shaped zonesexisting on the diffractive structure of the correcting elementsatisfies the following formula;15/k≦N2≦45/k where k is an order of diffracted light ray whosediffraction efficiency is higher than that of any one of other orderdiffracted light rays of the second light flux having a wavelength λ2.11. The optical pickup device of claim 7, wherein a sign of adiffracting power of the diffractive structure of the correcting elementis positive.
 12. The optical pickup device of claim 7, wherein thecorrecting element is arranged in an optical path through which only thefirst light flux emitted from the first light source passes, and whereinon the first spot formed on an information recording surface of thefirst optical information recording medium, a chromatic aberration ofthe converged spot caused by a change in a wavelength of a light sourceis regulated by the correcting element so as to be within a rangenecessary for recording and/reproducing of information, and on thesecond spot formed on an information recording surface of the secondoptical information recording medium, a chromatic aberration of theconverged spot caused by a change in a wavelength of a light source isregulated by the light converging optical element so as to be within arange necessary for recording and/reproducing of information.
 13. Theoptical pickup device of claim 12, wherein on the diffractive structureprovided on the light-converging optical element, the number N1 ofdiffractive ring-shaped zones existing on the area where both of thefirst and second light fluxes commonly pass when conducting recordingand/or reproducing of information for the first and second opticalinformation recording mediums satisfies the following formula;45/A≦N1≦65/A where A is 3m or 8p and is a order of diffracted light raywhose diffraction efficiency is higher than that of any one of otherorder diffracted light rays of the first light flux having a wavelengthλ1.
 14. The optical pickup device of claim 12, wherein the correctingelement comprises a diffractive structure on at least one opticalsurface thereof and the number N2 of diffractive ring-shaped zonesexisting on the diffractive structure of the correcting elementsatisfies the following formula;30/k≦N2≦80/k where k is an order of diffracted light ray whosediffraction efficiency is higher than that of any one of other orderdiffracted light rays of the second light flux having a wavelength λ2.15. The optical pickup device of claim 12, wherein a sign of adiffracting power of the diffractive structure of the correcting elementis negative.
 16. The optical pickup device of claim 12, wherein a signof a diffracting power of the diffractive structure of the correctingelement is positive.
 17. The optical pickup device of claim 1, whereinthe correcting element is arranged in an optical path through which thefirst light flux emitted from the first light source passes and in anoptical path through which the second light flux emitted from the secondlight source passes.
 18. The optical pickup device of claim 17, whereinon the first spot formed on an information recording surface of thefirst optical information recording medium and on the first spot formedon an information recording surface of the first optical informationrecording medium, a chromatic aberration of the converged spot caused bya change in a wavelength of a light source is regulated by the lightconverging optical element so as to be within a range necessary forrecording and/reproducing of information, and on the first spot formedon an information recording surface of the first optical informationrecording medium and on the first spot formed on an informationrecording surface of the first optical information recording medium, adeteriorated spherical aberration due to a change in temperature isregulated by the correcting element so as to be within a range necessaryfor recording and/reproducing of information.
 19. The optical pickupdevice of claim 18, wherein on the diffractive structure provided on thelight-converging optical element, the number N1 of diffractivering-shaped zones existing on the area where both of the first andsecond light fluxes commonly pass when conducting recording and/orreproducing of information for the first and second optical informationrecording mediums satisfies the following formula;144/(2n)≦N1≦176/(2n) where 2n is an order of diffracted light ray whosediffraction efficiency is higher than that of any one of other orderdiffracted light rays of the first light flux having a wavelength λ1.20. The optical pickup device of claim 18, wherein the correctingelement comprises a diffractive structure on at least one opticalsurface thereof and the number N2 of diffractive ring-shaped zonesexisting on the diffractive structure of the correcting elementsatisfies the following formula;30/k≦N2≦80/k where k is an order of diffracted light ray whosediffraction efficiency is higher than that of any one of other orderdiffracted light rays of the second light flux having a wavelength λ2.21. The optical pickup device of claim 1, wherein a focal length f1 ofthe light converging optical element for the first light flux from thefirst light source satisfies the following formula:1.8 mm≦f1≦3.0 mm.
 22. The optical pickup device of claim 1, wherein amagnification mt of an optical system in which the light convergingoptical element and the correcting element are combined satisfies thefollowing formula:⅓≦mt≦ 1/10.
 23. The optical pickup device of claim 1, wherein regulatinga deteriorated spherical aberration due to a wavelength change in alight source within a range necessary for recording and/or reproducingof information means that when a light source wavelength A changes by 10nm, a spherical aberration change amount of a wavefront aberration isregulated to be 0.065 arms or less.
 24. The optical pickup device ofclaim 1, wherein regulating a chromatic aberration on a converged spotdue to a wavelength change in a light source within a range necessaryfor recording and/or reproducing of information means that when a lightsource wavelength λ changes by 1 nm, a wavefront aberration at a bestimage forming position before the wavelength change is regulated to be0.02 arms or less.
 25. The optical pickup device of claim 1, whereinregulating a deteriorated spherical aberration due to a temperaturechange within a range necessary for recording and/or reproducing ofinformation means that when a temperature changes by 30° C., a sphericalaberration change amount of a wavefront aberration is regulated to be0.04 arms or less.
 26. The optical pickup device of claim 1, wherein thefollowing expression is satisfied when NA1 represents an image sidenumerical aperture of the light-converging optical element necessary forconducting recording and/or reproducing of information for the firstoptical information recording medium:0.63≦NA1≦0.67.
 27. The optical pickup device of claim 1, wherein thefollowing expression is satisfied when NA2 represents an image sidenumerical aperture of the light-converging optical element necessary forconducting recording and/or reproducing of information for the secondoptical information recording medium:0.63≦NA2≦0.67.
 28. The optical pickup device of claim 1, wherein thefollowing expression is satisfied when Δλ1/ΔT represents fluctuations ofa wavelength of the first light source for temperature:0.03 nm≦Δλ1/ΔT≦0.1 nm.
 29. The optical pickup device of claim 1, whereinthe following expression is satisfied when Δλ1/ΔT representsfluctuations of a wavelength of the second light source for temperature:0.15 nm≦Δλ2/ΔT≦0.25 nm.
 30. The optical pickup device of claim 1,further comprising: a third light source to emit a third light fluxhaving a wavelength λ3 (750 nm<λ3<800 nm), wherein the light-convergingoptical system converges a divergent light flux emitted from the thirdlight source on an information recording surface of the third opticalinformation recording medium through a protective layer having athickness t3 so that the optical pickup device conducts recording and/orreproducing information for a third information recording medium. 31.The optical pickup device of claim 30, wherein a optical systemmagnification mo of the light converging optical element for a incidentlight flux having a wavelength λ3 satisfies the following formula:1/12<mo< 1/14.
 32. The optical pickup device of claim 30, wherein adiffraction efficiency of (3m/2) th ((3m/2) represents an integer) orderdiffracted light ray becomes higher than a diffraction efficiency of anyone of other order diffracted light rays generated when the third lightflux emitted from the third light source passes through.
 33. The opticalpickup device of claim 30, wherein a diffraction efficiency of 4p-thorder diffracted light ray becomes higher than a diffraction efficiencyof any one of other order diffracted light rays generated when the thirdlight flux emitted from the third light source passes through.
 34. Theoptical pickup device of claim 30, wherein a diffraction efficiency ofn-th order diffracted light ray becomes higher than a diffractionefficiency of any one of other order diffracted light rays generatedwhen the third light flux emitted from the third light source passesthrough.
 35. The optical pickup device of claim 34, wherein the secondlight source and the third light source are arranged at a position wherea distance on an optical axis from the light converging optical elementis made equal.
 36. The optical pickup device of claim 30, furthercomprising: a coupling lens provided in a optical path on which only thethird light flux from the third light source passes and to change adivergent angle or a convergent angle of the third light flux from thethird light source.
 37. An optical pickup apparatus, comprising: a firstlight source to emit a first light flux having a wavelength λ1 (380nm<λ1<450 nm); and a light-converging optical system having alight-converging optical element including a diffractive structure and acorrecting element arranged between the first light source and thelight-converging optical element; wherein the light-converging opticalsystem converges the first light flux emitted from the first lightsource on an information recording surface of a first opticalinformation recording medium through a protective layer having athickness t1 so that the optical pickup device conducts recording and/orreproducing information for the first information recording medium, andwherein on a first spot formed on the information recording surface ofthe first optical information recording medium, a deteriorated sphericalaberration due to a wavelength change in the first light source and adeteriorated spherical aberration due to a temperature change areregulated to be within a range necessary for recording and/orreproducing of information.
 38. The optical pickup device of claim 37,wherein a diffractive structure is provided on a area on a part of atleast one optical surface of the light converging optical element, andwhen the order of a diffracted ray whose diffraction efficiency is thelargest among other order diffracted light rays generated when the firstlight flux emitted from the first light source passes through thediffractive structure of the light converging optical element is KBOLand the number of ring-shaped zones of the diffractive structure of thelight converging element is nBOL, the following formula is satisfied:30<nBOL·KBOL<130.
 39. The optical pickup device of claim 37, wherein adiffractive structure is provided on a area on a part of at least oneoptical surface of the correcting element, and when the order of adiffracted ray whose diffraction efficiency is the largest among otherorder diffracted light rays generated when the first light flux emittedfrom the first light source passes through the diffractive structure ofthe correcting element is KCOL and the number of ring-shaped zones ofthe diffractive structure of the light converging element is nCOL, thefollowing formula is satisfied:30<nCOL·KCOL<130.
 40. The optical pickup device of claim 37, wherein onthe first spot formed on the information recording surface of the firstoptical information recording medium, a chromatic aberration of theconverged spot caused by a change in a wavelength of a light source isregulated to be within a range necessary for recording and/reproducingof information.
 41. The optical pickup device of claim 37, wherein thethickness t1 of the protective layer of the first optical informationrecording medium satisfies the following formula:0.5 mm≦t1≦0.7 mm.
 42. The optical pickup device of claim 37, wherein afocal length f1 of the light converging optical element for the firstlight flux from the first light source satisfies the following formula:1.8 mm≦f1≦3.0 mm.
 43. The optical pickup device of claim 37, wherein amagnification mt of an optical system in which the light convergingoptical element and the correcting element are combined satisfies thefollowing formula:⅓≦mt≦ 1/10.
 44. The optical pickup device of claim 37, whereinregulating a deteriorated spherical aberration due to a wavelengthchange in a light source within a range necessary for recording and/orreproducing of information means that when a light source wavelength λchanges by 10 nm, a spherical aberration change amount of a wavefrontaberration is regulated to be 0.07 arms or less.
 45. The optical pickupdevice of claim 37, wherein regulating a chromatic aberration on aconverged spot due to a wavelength change in a light source within arange necessary for recording and/or reproducing of information meansthat when a light source wavelength A changes by 1 nm, a wavefrontaberration at a best image forming position before the wavelength changeis regulated to be 0.02 λ rms or less.
 46. The optical pickup device ofclaim 37, wherein regulating a deteriorated spherical aberration due toa temperature change within a range necessary for recording and/orreproducing of information means that when a temperature changes by 30°C., a spherical aberration change amount of a wavefront aberration isregulated to be 0.04 λ rms or less.
 47. The optical pickup device ofclaim 37, wherein the following expression is satisfied when NA1represents an image side numerical aperture of the light-convergingoptical element necessary for conducting recording and/or reproducing ofinformation for the first optical information recording medium:0.63≦NA1≦0.67.
 48. The optical pickup device of claim 37, wherein thefollowing expression is satisfied when Δλ1/ΔT represents fluctuations ofa wavelength of the first light source for temperature:0.03 nm≦Δλ1/ΔT≦0.1 nm.
 49. A light converging optical element for use inan optical pickup apparatus which comprises: a first light source toemit a first light flux having a wavelength λ1 (380 nm<λ1<450 nm); asecond light source to emit a second light flux having a wavelength λ2(600 nm<λ2<700 nm); and a light-converging optical system having alight-converging optical element including a diffractive structure and acorrecting element arranged between the first light source and/or thesecond light source and the light-converging optical element; whereinthe light-converging optical system converges the first light fluxemitted from the first light source on an information recording surfaceof a first optical information recording medium through a protectivelayer having a thickness t1 so that the optical pickup device conductsrecording and/or reproducing information for the first informationrecording medium and the light-converging optical system converges thesecond light flux emitted from the second light source on an informationrecording surface of a second optical information recording mediumthrough a protective layer having a thickness t2 so that the opticalpickup device conducts recording and/or reproducing information for thesecond information recording medium, the converging optical elementcomprising: a diffractive element; wherein the light-converging opticalsystem generates N-th order diffracted light ray when the first lightflux from the first light source passes through the diffractivestructure so that the light-converging optical system forms a first spoton the information recording surface of the first optical informationrecording medium by using the N-th order diffracted light ray, whereinthe converging optical element generates M-th order (M≠N) diffractedlight ray when the second light source passes through the diffractivestructure so that the light-converging optical system forms a secondspot on the information recording surface of the second opticalinformation recording medium by using M-th order (M≠N) diffracted lightray, wherein on the first spot formed on the information recordingsurface of the first optical information recording medium, adeteriorated spherical aberration due to a wavelength change in thefirst light source and a deteriorated spherical aberration due to atemperature change are regulated to be within a range necessary forrecording and/or reproducing of information, and on the second spotformed on the information recording surface of the second opticalinformation recording medium, a deteriorated spherical aberration due toa wavelength change in the second light source and a deterioratedspherical aberration due to a temperature change are regulated to bewithin a range necessary for recording and/or reproducing ofinformation.
 50. A light converging optical element for use in anoptical pickup apparatus which comprises: a first light source to emit afirst light flux having a wavelength λ1 (380 nm<λ1<450 nm); and alight-converging optical system having a light-converging opticalelement including a diffractive structure and a correcting elementarranged between the first light source and the light-converging opticalelement; wherein the light-converging optical system converges the firstlight flux emitted from the first light source on an informationrecording surface of a first optical information recording mediumthrough a protective layer having a thickness t1 so that the opticalpickup device conducts recording and/or reproducing information for thefirst information recording medium, the light converging opticalelement, comprising: a diffractive structure; wherein on a first spotformed on the information recording surface of the first opticalinformation recording medium, a deteriorated spherical aberration due toa wavelength chance in the first light source and a deterioratedspherical aberration due to a temperature change are regulated to bewithin a range necessary for recording and/or reproducing ofinformation.
 51. A correcting element for use in an optical pickupapparatus which comprises: a first light source to emit a first lightflux having a wavelength λ1 (380 nm<λ1<450 nm); a second light source toemit a second light flux having a wavelength λ2 (600 nm <λ2<700 nm); anda light-converging optical system having a light-converging opticalelement including a diffractive structure and a correcting elementarranged between the first light source and/or the second light sourceand the light-converging optical element; wherein the light-convergingoptical system converges the first light flux emitted from the firstlight source on an information recording surface of a first opticalinformation recording medium through a protective layer having athickness t1 so that the optical pickup device conducts recording and/orreproducing information for the first information recording medium andthe light-converging optical system converges the second light fluxemitted from the second light source on an information recording surfaceof a second optical information recording medium through a protectivelayer having a thickness t2 so that the optical pickup device conductsrecording and/or reproducing information for the second informationrecording medium, the correcting element arranged between the firstlight source and/or the second light source and the light-convergingoptical element, wherein the light-converging optical system forms afirst spot on the information recording surface of the first opticalinformation recording medium by using N-th order diffracted light raygenerated when the first light flux from the first light source passesthrough the diffractive structure of the light-converging opticalsystem, and the light-converging optical system forms a second spot onthe information recording surface of the second optical informationrecording medium by using M-th order (M≠N) diffracted light raygenerated when the second light flux from the second light source passesthrough the diffractive structure of the light-converging opticalsystem, and wherein on the first spot formed on the informationrecording surface of the first optical information recording medium, adeteriorated spherical aberration due to a wavelength change in thefirst light source and a deteriorated spherical aberration due to atemperature change are regulated to be within a range necessary forrecording and/or reproducing of information, and on the second spotformed on the information recording surface of the second opticalinformation recording medium, a deteriorated spherical aberration due toa wavelength change in the second light source and a deterioratedspherical aberration due to a temperature change are regulated to bewithin a range necessary for recording and/or reproducing ofinformation.
 52. A light converging optical element for use in anoptical pickup apparatus which comprises: a first light source to emit afirst light flux having a wavelength λ1 (380 nm<λ1<450 nm); and alight-converging optical system having a light-converging opticalelement including a diffractive structure and a correcting elementarranged between the first light source and the light-converging opticalelement; wherein the light-converging optical system converges the firstlight flux emitted from the first light source on an informationrecording surface of a first optical information recording mediumthrough a protective layer having a thickness t1 so that the opticalpickup device conducts recording and/or reproducing information for thefirst information recording medium, the correcting element arrangedbetween the first light source and the light-converging optical element;wherein on a first spot formed on the information recording surface ofthe first optical information recording medium, a deteriorated sphericalaberration due to a wavelength change in the first light source and adeteriorated spherical aberration due to a temperature change areregulated to be within a range necessary for recording and/orreproducing of information.